1. Field of the Invention
This invention relates to a method for automatically reducing the drawing speed of a tubular material drawing block machine. The drawing block machine is employed for drawing tubular material, or similar items. The invention is employed to slow the speed of the machine before the end of drawing of a coil of tubular material. With this drawing process, each of several tubular material coils is drawn through a drawing die, in succession. The drawn tubular material is, then, collected in a collecting basket. The collecting basket is, then, transported to a pay-out station. The drawn tubular material is then re-drawn one or more times until the desired diameter and wall thickness, of the tubular material, is achieved.
2. Background Information
Initially, it is to be understood that, as recited in the specification and claims, the term "tubular material" may include rods, wire, and/or tubes, or the like.
Continuous drum drawing machines, for tubular material, are frequently known as drawing or spinner blocks. One example of such a machine may be found in U.S. Pat. No. 4,890,470, entitled "Loop Transport System For A Plurality Of Baskets Containing Material To Be Drawn Through A Drawing Machine." The drawing force of the drawing block, or drum, is supplied by the friction between the block and the tubular material since the tubular material is wrapped, generally, five to ten times around the drum and supported by non-driven idler rollers that press the tubular material against the exterior surface of the drum. As the tubular material accumulates on the drum, the uppermost portions of the tubular material exert a continuous downward pressure on the portions of the tubular material below so that the lower portions are discharged into a receiving basket.
The receiving basket is configured to an appropriate size so that the largest possible coil weight can be held to allow a long length of tubular material to be kept in a single, continuous length, even when the tubular material is drawn to extremely small dimensions.
Tubes are reduced in several passes. For example, a size 55.times.2.5 mm tubular material having a unit weight of 300 kg, may be reduced to size 6.times.0.35 mm for example. The resulting tubular material, in this example, is 5,450 m long. Such dimensions mean that the tubular material has an initial diameter of 55 mm and an initial wall thickness of 2.5 mm, while the final dimensions may be a diameter of 6 mm and a wall thickness of 0.35 mm.
After one pass through the machine, the receiving basket, loaded with drawn tubular material, is transported from its position underneath the drawing block, to a pay-out station. The tubular material is then guided back through the machine for another pass through the drawing die and around the drawing block, after a new, empty receiving basket is placed under the drawing block at the receiving station. Generally, six to seven coils of tubular material are processed as a group, in succession until all coils in the group have been finally reduced.
If only a few turns of tubular material remain in the basket at the pay-out station, the drawing speed, of the machine, must be reduced so that the end of the tubular material does not thrash back and forth, in an uncontrolled manner, when leaving the pay-out basket and, also, so that the end of the tubular material does not jump out of the basket. Also, jerk of the tubular material, which may occur when the tubular material is discharged from the drawing die and the friction between the tubular material and the drum disappears, is sharply decreased. The maximum attainable drawing speed is, currently, about 1,200 m/minute. A reduction of this drawing speed to approximately 60 m/min., at the end of the drawing pass, is desirable to prevent the above described problems.
In prior art machines, the reduction of the speed of rotation, when there are only a few number of turns of tubular material remaining in the pay-out basket, is performed by the operator, who observes the number of turns remaining in the pay-out basket by means of one or more mirrors. When there are only a few turns remaining in the basket, the operator activates a control to reduce the speed. The remaining turns are then drawn at the reduced speed, for the reasons indicated above. This activity occupies the operator during a portion of the drawing process so that he cannot do other work.
The need to automate the spinner block process, thereby freeing up the operator for other duties, has led to the idea of counting the turns of tubular material that fall into the receiving basket and storing that value in a computer with a memory counter. When the basket is again in the pay-out station, during the next drawing sequence, the falling turns are again recorded by the computer and the drawing speed is reduced when a certain number of turns have fallen into the basket. However, the computer must mathematically adjust the number of turns by the elongation which occurs during reduction of the tubular material in the drawing die. Another factor, for which a mathematical adjustment should be, but usually is not, made, includes fluctuating tubular material weight, per unit of length, which is a function of the condition of the drawing die. Different tubular material weights result in varying tubular material lengths and numbers of turns of tubular material after the drawing process. With a hypothetical weight fluctuation of plus/minus 5% and a nominal length of 5,000 m, the fluctuations would be plus/minus 250 m. If we take these possible errors into consideration, by programming the computer for the smallest possible number of turns of tubular material then, with the maximum tubular material length possible, an additional 500 m would be drawn at the reduced drawing speed. The average drawing speed is, thereby, severely decreased and the drawing time becomes correspondingly longer.
In another process of the prior art, after several turns of the tubular material are drawn, the tubular material is marked with a dye or paint. During the next pass, this marking is detected by sensors and used as a signal to reduce the speed of the drawing block drive. This process takes advantage of the fact that the beginning of the tubular material that falls into the receiving basket, first, becomes the end of the tubular material in the next pass. This process has not been implemented, in actual practice, because no suitable marking inks, dyes or paints exist, on the market, which guarantee the optical detection of the end segment of the tubular material.